Among methods for producing an acylamino acid, the acylamino acid containing impurities as little as possible may be obtained by reacting a carboxylic acid corresponding to an acyl group with an amino acid ester in the presence of a condensing agent such as dicyclohexylcarbodiimide (DCC) and then hydrolyzing the ester. However, because the method requires preparation of an amino acid ester once and usage of an expensive condensing agent, it has a disadvantage in high production cost.
As regards another method for producing an acylamino acid, which uses an amino acid instead for an amino acid ester, it is known that the acylamino acid may be obtained by reacting a carboxylic acid with N-hydroxy succinimide in the presence of DCC and the like to form an activated ester, and then reacting the activated ester with an amino acid. However, because the method also requires usage of an expensive condensing agent and its yield is not high, it raises the production cost.
At present, as regards the method for producing an acylamino acid at low cost, Schotten-Baumann reaction is considered to be the most industrially-superior reaction, wherein an acid chloride and an amino acid are reacted in an aqueous solvent under the alkali condition. The reaction is used for the production of various acylamino acids.
Though Schotten-Baumann reaction tried to be applied to the production of acylphenylalanine, it was found that impurities were produced in the reaction and they were not easily removed.